The parents of Otto Warmbier, the American student who died in June shortly after being released from a North Korea prison, are urging lawmakers to designate the isolated country as a state sponsor of terrorism.

Following pressure from Fred and Cindy Warmbier, 12 senators – six Democrats and six Republicans – issued a letter to Secretary of State Rex Tillerson, asking that North Korea be added to the list of terrorism sponsors.

There are currently three countries on the list - Iran, Syria and Sudan. North Korea was on it from 1988 to 2008 until it was taken off by the George W. Bush administration, as part of a deal to freeze North Korea's nuclear weapons program.

Republican Sen. Rob Portman from Ohio said Wednesday that North Korea has a history of failing to comply with international agreements.

"Of course North Korea didn’t follow through on the commitments they had made on the nuclear program, and yet this designation never was renewed," he said.